This invention is a result of a contract with the United States Department of Energy. It relates generally to the art of thermochemical hydrogen production.
Hydrogen is presently considered to be an attractive energy agent to be developed for future use. Hydrogen has many attributes which make it a logical replacement for fossil fuels which are being rapidly consumed and increasingly expensive. The combustion of hydrogen produces no obnoxious products and thus no harm to the environment.
Existing energy transport means and energy consuming equipment can be adapted to a hydrogen-based energy system using technology presently available. Natural gas pipelines, for example, can be converted to hydrogen carrying pipelines with minor modifications. Experimental automobiles are presently operating with modified conventional internal combustion engines using hydrogen as a fuel.
As the prospect of hydrogen utilization becomes increasingly likely, means for producing hydrogen need to be upgraded and increased. Conventionally, hydrogen has been produced by the electrolysis of water. Electrolysis, however, is highly inefficient in view of the less than 40 percent efficiency of electricity production coupled with an efficiency of about 80 percent for electrolysis. Inherent in the electrolytic production of hydrogen is the general futility of using one energy source, typically fossil fuels at present, to produce electricity which is then ultimately used to produce hydrogen at the point of electrolysis. The disadvantages of excess consumption of fossil fuels are obviously not overcome by such a process.
Chemical processes for the direct conversion of fossil fuels and water into hydrogen are presently feasible technically and overcome many of the inefficiencies and disadvantages of electrolysis. However, prudence indicates that fossil fuels should be preserved as much as possible for long term pharmaceutical, chemical and metallurgical uses.
Thermochemical processing presents the most attractive method for producing hydrogen. Using this technique, water is broken down into hydrogen and oxygen by a series of chemical reactions not involving the use of fossil fuels. This series of reactions is preferably carried out in a closed cyclic manner in which all products except hydrogen and oxygen are reused as reactants in the other reactions. One such process, disclosed in U.S. Pat. No. 3,490,871, utilizes the reaction of cesium with water to release hydrogen.
Another such process, disclosed by Grimes et al in U.S. Pat. No. 3,919,406, involves the reaction of copper and magnesium chlorides with water to produce hydrogen in a closed cyclic manner.
Another such process is disclosed by Bamberger et al in U.S. Pat. No. 3,927,192. The process therein disclosed comprises reacting chromium oxide with an alkali metal hydroxide to produce hydrogen, water and alkali metal chromate as reaction products.
Bamberger et al (U.S. Pat. No. 3,929,979) also disclose a cyclic process for splitting water wherein magnetite is reacted with an alkali metal hydroxide to give hydrogen, alkali metal ferrate and water as products.
Bamberger et al, in U.S. Pat. No. 3,996,343, disclose the production of hydrogen in a closed chemical cycle for the thermal decomposition of water by reaction of water with chromium sesquioxide and strontium oxide.
Bamberger et al (U.S. Pat. No. 4,005,184) employ chromium and barium compounds in a thermochemical process for producing hydrogen using barium and chromium compounds.
Ishii et al (U.S. Pat. No. 4,098,875) produce hydrogen thermochemically from water using tri-iron tetraoxide and hydrogen bromide as the main cyclic reaction media. The use of barium iodide, carbon dioxide and ammonia as cyclic reaction media is disclosed in U.S. Pat. No. 3,996,342.